The use of polymeric film bases for carrying photographic layers is well known. In particular, photographic elements which require accurate physical characteristics use polyester film bases, such as polyethyleneterephthalate film bases, and cellulose ester film bases, such as cellulose triacetate film bases.
The formation of static electric charges on the film base is a serious problem in the production of photographic elements. While coating the light-sensitive emulsion, electric charges which accumulate on the base discharge, producing light which is recorded as an image on the light-sensitive layer. Other drawbacks which result from the accumulation of electric charges on polymeric film bases are the adherence of dust and dirt, coating defects and limitation of coating speed.
Additionally, photographic elements comprising light-sensitive layers coated onto polymeric film bases, when used in rolls or reels, which are mechanically wound and unwound, or in sheets, which are conveyed at high speed, tend to accumulate static charges and record the light generated by static discharges. Moreover, charge buildup can create difficulties in processing, such as jamming as the photographic films are fed through processing equipment.
The static-related damages occur not only before the photographic element has been manufactured, exposed and processed, but also after processing when the photographic element including the image is used to reproduce and enlarge the image. Accordingly, it is desired to provide permanent antistatic protection which retains its effectiveness even after processing.
To overcome the adverse effects resulting from accumulation of static electrical charges, photographic elements are provided with antistatic layers including electrically conductive materials which are capable of transporting charges away from areas where they are not desired. Typically, such antistatic layers contain electrically conductive substances, in particular polyelectrolytes such as the alkali metal salts of polycarboxylic acids or polysulfonic acids, or quaternary ammonium polymers, which dissipate the electrical charge by providing a surface which conducts electricity by an ionic mechanism. However, such layers are not very suitable as antistatic layers because they lose effectiveness under conditions of low relative humidity, become sticky under conditions of high relative humidity, and lose the antistatic effect after passage through photographic processing baths.
Antistatic materials that conduct electrons by a quantum mechanical mechanism rather than ions by an ionic mechanism are preferred because antistatic materials that conduct electrons by a quantum mechanical mechanism are effectively independent of humidity. They are suitable for use under conditions of low relative humidity, without losing effectiveness, and under conditions of high relative humidity, without becoming sticky. Defect semiconductor oxides and conductive polymers have been proposed as electronic conductors which operate independent of humidity. A major problem, however, with defect electronic conductors is that they generally cannot be provided as thin, transparent, relatively colorless coatings by solution coating methods.
Vanadium oxide antistatic coatings have been taught for use in photographic elements. U.S. Pat. No. 4,203,769 discloses a radiation-sensitive element comprising an antistatic layer of amorphous vanadium oxide. The antistatic layer can contain only vanadium oxide or the vanadium oxide may be dispersed in a binder. The amorphous vanadium oxide solution is prepared by heating the vanadium oxide to at least 100.degree. C. above its melting point and casting the molten mass into a solubilizing amount of water. The vanadium oxide to binder weight ratio ranges up to about 1:7.
In photographic elements, the antistatic layer comprising vanadium oxide can be located on the side of the film base opposite to the image-forming layer as outermost layer, with or without a protective abrasion-resistant topcoat layer, or can be located as a subbing layer underlying a silver halide emulsion layer or an auxiliary gelatin layer. U.S. Pat. No. 5,221,598 indicates that vinylidene chloride/itaconic acid/methyl acrylate terpolymers and the like may be used as the polymeric binder for the antistatic layer. According to this patent, binder to vanadium oxide ratios can range from 1:5 to 200:1, but preferably are in the range from 1:1 to 10:1. U.S. Pat. No. 5,360,706 notes that when vinylidene chloride terpolymers are used with low amounts of vanadium oxide flocculation of the coating solution becomes a problem.
U.S. Pat. No. 5,006,451 and 5,221,598 describe a photographic material comprising a film base having thereon an antistatic layer comprising vanadium oxide and a barrier layer which overlies the antistatic layer. These patents report that the barrier layer is necessary to prevent the vanadium oxide from diffusing out of the underlying antistatic layer. See also U.S. Pat. No. 5,447,832, Example 26, which teaches that the antistatic properties of the vanadium oxide layer are destroyed after film processing if the vanadium oxide layer is not protected by an impermeable barrier. In addition, the use of a barrier layer is taught to be advantageous in that it provides excellent adhesion between the emulsion layer and the antistatic layer. Unfortunately, the solution provided by said patent requires a two-layer antistatic construction which requires additional investment and operating cost.
Accordingly, there is still the need to provide single layer antistatic layers, using vanadium oxide, which give permanent antistatic protection in photographic processing solutions.